Various optical materials have been employed to provide authentication of currency and documents, to identify and distinguish authentic products from counterfeit products, and to provide visual enhancement of manufactured articles and packaging. The evolution of such material stems largely from the search for a mechanism to resist counterfeiting of certain articles and products, or alternatively to render such copying obvious. Examples of optical materials used in anti-counterfeiting applications include holographic displays, as well as image systems that rely on lenticular structures or arrays of micro-lenses to project images that exhibit optical effects which cannot be reproduced using traditional printing and/or photocopying processes.
Optical materials based upon the concept of moiré magnification are particularly attractive for use in anti-counterfeiting applications. Such materials typically include a top lens layer, an intermediate substrate (an optical spacer), and a bottom print or object layer which contains micro-object(s) that are to be magnified or otherwise altered when viewed through the lenses. Such materials can create attractive visual effects that can be desirable in anti-counterfeiting and aesthetic applications.
While existing optical materials can produce a variety of visual effects, new optical materials are continually needed to stay ahead of the counterfeiter's ability to access or develop new imaging technologies.